Semiconductor devices go through various processes before being completed as products. Various abnormalities during processing in such processes cause a decrease in yield or a decrease in quality. The semiconductor device manufacturing method includes an inking process where the acceptability of chips are determined by conducting an electrical characteristic test (wafer test) on the chips formed on a wafer on a chip-by-chip basis after forming patterns on the wafer in various processes and defective chips are marked with ink. The marking of defective chips depends on the results of the wafer test. It is empirically known, however, that if there is a concentration of defective chips in their distribution (a defective distribution concentration), that is, if defective chips concentrate on part of the wafer, it is impossible to guarantee the quality of chips adjacent to or in the neighborhood of the concentration of defective chips to a sufficient extent even if the adjacent or neighboring chips have been determined as acceptable (not defective) in the wafer test. In particular, if those chips are located at or near the periphery of the wafer, it is more difficult to guarantee their quality.
Therefore, conventionally, wafers having a defective distribution concentration are discarded, thereby guaranteeing the quality of products. The discarding of wafers, however, inevitably causes loss. Further, this loss tends to increase with a recent increase in the size of wafers.
Even if there is a concentration of defective chips in their distribution on a wafer, chips whose quality can be guaranteed to a sufficient extent may be present on the same wafer depending on the distribution of the defective chips. There are various forms of abnormality. For example, there are abnormalities whose effects depend on the separation of chips, such as insufficient exposure in a shot by a stepper in the photolithography process. However, most of the abnormalities such as those due to abnormal discharge in the etching process are independent of the separation of chips. Further, the effects of most of the abnormalities independent of the separation of chips tend to be inversely proportional to the distance from the center of a defective distribution concentration.
In order to save such wafers, the wafer test result is visually confirmed, and acceptable chips adjacent to or in the neighborhood of a defective distribution concentration are regarded as defective chips and marked to be recognized as defective. Hereinafter, the operation of marking chips determined as acceptable in a wafer test but difficult to guarantee in quality, such as acceptable chips adjacent to or in the neighborhood of a defective distribution concentration, in order to recognize such chips as defective is referred to as additional inking.
Additional inking may be carried out by directly inking a wafer or processing a wafer test result. It is common practice to employ the former in the case of using the inker function of a test prober and the latter in the case of performing inking with a prober dedicated to inking (hereinafter, referred to as a marking prober) without using the inker function of the test prober.
According to the method of directly inking the wafer, additional inking is performed on chips that seem to have quality problems while looking at the wafer test result or the inked wafer itself.
According to the method of processing the wafer test result, additional inking is performed on chips that seem to have quality problems while looking at the data of the wafer test displayed on a screen by dedicated software (program).
Further, in these years, inkless methods may be employed that perform processing in a subsequent process based on the electronic information of wafer test results without marking (inking) defective chips. In the case of inkless methods, the operation of changing the electronic information of acceptable chips whose quality is difficult to guarantee to electronic information indicating defective chips in the electronic information of the wafer test result is also referred to as additional inking.
The quality of chips is guaranteed by such operations. However, there is a problem in that selection of potentially defective chips for performing additional inking, which is performed based on experience-based sensory determinations, differs between individuals. Further, selection of potentially defective chips takes a large number of man-hours, which tend to increase with an increase in the size of wafers.
Japanese Patent No. 3888938 proposes an algorithm for solving such problems, which analyzes the distribution of defectives within a wafer and predicts chips that may have problems in quality. This algorithm has improved additional inking.